Abstract
During an eight-hour shift, an industrial worker will inevitably cycle through specific postures. Those postures can cause microtrauma on the musculoskeletal system that accumulates, which in turn can lead to chronic injury. To assess how problematic a posture is, the rapid upper limb assessment (RULA) scoring system is widely employed by the industry. Even though it is a very quick and efficient method of assessment, RULA is not a biomechanics-based measurement that is anchored in a physical parameter of the human body. As such RULA does not give a detailed description of the impact each posture has on the human joints but rather, an overarching, simplified assessment of a posture. To address this issue, this paper proposes the use of joint angles and torques as an alternative way of ergonomics evaluation. The cumulative motion and torque throughout a trial is compared with the average motions and torques for the same task. This allows the evaluation of each joint’s kinematic and kinetic performance while still be able to assess a task“at-a-glance”. To do this, an upper human body model was created and the mass of each segment were assigned. The joint torques and the RULA scores were calculated for simple range of motion (ROM) tasks, as well as actual tasks from a TV assembly line. The joint angles and torques series were integrated and then normalized to give the kinematic and kinetic contribution of each joint during a task as a percentage. This made possible to examine each joint’s strain during each task as well as highlight joints that need to be more closely examined. Results show how the joint angles and torques can identify which joint is moving more and which one is under the most strain during a task. It was also possible to compare the performance of a task with the average performance and identify deviations that may imply improper execution. Even though the RULA is a very fast and concise assessment tool, it leaves little room for further analyses. However, the proposed work suggests a richer alternative without sacrificing the benefit of a quick evaluation. The biggest limitation of this work is that a pool of proper executions needs to be recorded for each task before individual comparisons can be done.
Highlights
In the industry, physical exertion is required for productivity to remain at an acceptable level
work-related musculoskeletal disorders (WMSDs) are not clinically different from other musculoskeletal disorders, such as overuse syndrome on the prosthesis users’ population, in the sense that their cause is that there is not enough time for the tissues to recover from repeated motions
The forearm flexion/extension task required the participants to stand, flex their forearms to a mid-position somewhere in the middle of their range of motion (ROM), hold them for a couple of seconds, flex their forearms until they are perpendicular to the ground with their fingers, and extend them to their original position
Summary
Physical exertion is required for productivity to remain at an acceptable level. The ergonomics risk factors that can lead to WMSDs are repetition, force, awkward postures, vibrations, contact stress, static loading (Jaffar et al 2011). The existence of any or all of those aspects doesn’t necessarily lead to WMSDs if their occurrence is not very frequent As it was mentioned, it’s the long exposures to these risk factors and the insufficient rest time in-between that can lead to WMSDs. As it was mentioned, it’s the long exposures to these risk factors and the insufficient rest time in-between that can lead to WMSDs It is not apparent which occupations have a higher probability to cause WMSDs. For example, employees in the food services have reported higher discomfort levels than those in the manufacturing industry (Oakman and Chan 2015). Such an unintuitive observation highlights that ergonomics risk factors need to be measured in an objective way
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